Process for manufacturing compostible thin-walled molded articles based on starch

ABSTRACT

With a process for manufacturing compostible thin-walled molded articles such as cups, plates, fast-food packagings, trays, flat sheets and the like, by applying a starch-based baking composition on the lower part of a multipart, preferably bipartite mold, to obtain a tough, durable article of high mechanical stability by using an essentially fat-free baking composition composed of water, a starch product, a release agent, and optionally further conventional additives, by baking the baking composition filling the mold, and by conditioning the resulting product to establish a moisture content of 6-22% by weight, the invention proposes the use, in addition to or instead of starch, of at least one modified starch selected from the group comprising starch esterified with organic acids or phosphoric acid, etherified starch, cross-linked starch and starch capable of being modified by ionic interaction.

BACKGROUND OF THE INVENTION

The present invention relates to a process for manufacturing compostible thin-walled molded articles such as cups, plates, fast-food packagings, trays, flat sheets and the like, by applying a starch-based baking composition on the lower part of a multipart, preferably bipartite mold, to obtain a tough, durable article of high mechanical stability

1) by using an essentially fat-free baking composition that is composed of

a) 42.0-60.0% by weight, preferably 45.0-56.0% by weight, water,

b) 36.0-56.5% by weight, preferably 38.0-52.0% by weight, of a starch product

c) 0.04-11% by weight, preferably 0.2-4.5% by weight, of one or more medium- or long-chain, optionally substituted fatty acids and/or salts thereof and/or acid derivatives thereof, e.g. acid amides, as a release agent--optionally using 0.5-6.5% by weight, preferably 0.1-4.2% by weight, of polymethylhydrogen siloxanes in combination with said compounds, or as a partial or occasionally as a complete substitute thereof, such that, when both groups of compounds are used and the concentrations of fatty acids and derivatives thereof are high, normally the concentration of polymethylhydrogen siloxanes is best not allowed to exceed 3% by weight, and optionally thickening agents such as swell-starch, pregelatinized starch or baking wastes, and/or guar gum, pectin, carob gum, carboxymethylcellulose and/or gum arabic; fibrous materials such as high-cellulose raw materials, vegetable raw materials, fibers of plastics, glass, metal and carbon; non-fibrous fillers such as calcium carbonate, carbon, talc, titanium dioxide, silica gel, alumina, shellac, soybean protein powder, wheat gluten powder, chicken egg protein powder, casein powder, and caseinate powder; colorants; preservatives and antioxidants;

2) by baking the baking composition filling the mold, and

3) by conditioning the resulting product to establish a moisture content of 6-22% by weight.

Such a process is described in our U.S. Pat. No. 5,376,320. Various starches and/or flours and flour mixtures are used as starch products there.

SUMMARY OF THE INVENTION

The type of starch used to produce the molded articles together with the co-use of additives and the manufacturing conditions determine the properties (weight, density, mechanical properties and the like) of the resulting product.

It has surprisingly been found that the molded articles show significantly increased stability when in addition to or in lieu of starch at least one modified starch chosen from the group comprising starch esterified with organic acids or phosphoric acid, etherified starch, cross-linked starch and starch capable of being modified by ionic interaction is used.

While the starch derivatives used to date in the known formulations have been employed mainly because of their thickening action, e.g. pregelatinized starch, thereby keeping a check on sedimentation of individual ingredients of the baking composition, the additives of the invention are found to have an effect on structure formation and stability.

Starch, most important natural starches consisting of amylose (17-31%) and amylopectin (69-83%), is organized in granular structure, one grain consisting of a large number of amylose and amylopectin molecules of high chain length (greater than 1000 glucose units). Per glucose unit 3 OH groups of amylose are available for substitution, equally so with amylopectin, with the exception of the branching positions, here 2 free OH.

Starch derivatives are characterized by several important indicators:

DS (degree of substitution) average number of substituted positions per glucose unit Maximum=3, frequently used from less than 0.001 to 0.2, i.e. less than 1 to 200 substituted positions per 1000 glucose units % substitution (% by weight substituents in total dry substance)

Indication of DS or % substitution is depending on method of derivatization and determinability.

The said starch derivatives (esterified starch, etherified starch and cross-linked starch) are outwardly (microscopically) unchanged granules of starch. They must show two mutually balanced activities.

1. Facilitation of swelling of the grain by monofunctional esterification, etherification i.e. water binding and gelatinization at lower temperatures. Consequence: faster, further-reaching gelatinization during the baking process, thus better exploitation of the "binding force" of starch.

2. Cross-linking of grain structures limiting swelling, water is absorbed and retained, but no unlimited swelling and thus bursting of the grain. A denser and more stable structure as a result.

1a) esterification with organic acids: ##STR1##

R=CH₃ acetylation, DS up to 0.12

R=CH₂ --CH₂ --COOR₁ succinylation, max. 4% succinic anhydride

R₁ =H, Na or other counterion, depending on pH and salts/bases used

R=CHR₂ --CHR₃ --COOR₁, alkenyl succinylation, max. 3% alkenyl succinic anhydride

R₂ =H and R₃ =alkenyl or

R₂ =alkenyl and R₃ =H

Alkenyl=Octenyl, decenyl for example

    ______________________________________                                         Example:                                                                                               Gelatinization                                                                 temperature                                            ______________________________________                                         Corn starch             62-72° C.                                       acetylation at DS                                                                               0.04   56-63° C.                                                        0.08   48-56° C.                                       (R = COCH.sub.3) 0.12   41-51° C.                                       ______________________________________                                          (Leach et. al, Cer. Chem 36, 564, 1959)                                  

    Example: succinic acid ester                                                                 Gelatinization                                                                            Swelling                                                            temp.      at room temp.                                         % substitution                                                                               degrees C. ml/25 g                                               ______________________________________                                         0             72         34                                                    1             67         35                                                    2             65         40                                                    3             63         47                                                    4             58         49                                                    ______________________________________                                          (O. B. Wurzburg, Modified starches, CRC Press, 1986, p. 133)             

The esters are not stable under alkaline conditions, therefore etherification is preferable.

1b) Monofunctional esterification with phosphoric acid: ##STR2##

R=H, Na or other counterion, depending on pH and salts/bases used

DS=0.005-0.1, preferably less than 0.05, max. 0.5% P in the derivative; from approximately DS 0.07 upwards gelatinization at room temperature.

1c) Etherification: starch--OH→starch--O--R

R=CH₂ --CH₂ --OH hydroxyethyl ether

R=(CH₂)₃ --OH hydroxypropyl ether

DS=0.01-0.2, preferably 0.02 to 0.1

The substitution effects described apply in principle to all important types of starch (corn, potato, tapioca, wheat) as well as to cationic starches.

The influence of cross-linking is of particular importance with potato starch, as it shows extreme swelling and dissolution of the granular structure.

    ______________________________________                                                water      mean aggregate                                                      absorption volume     packing                                                  g/g starch ml/g       density                                           ______________________________________                                         corn     15.1         35.5       0.45                                          potato   115.0        405.0      0.24                                          tapioca  21.9         59.5       0.38                                          ______________________________________                                          (Evans, Haisman, J. Texture Studies 10, 347, 1979)                       

2) Cross-linking:

1. Phosphate cross-linking with sodium trimetaphosphate or phosphorus oxychloride ##STR3## R=H, Na or other counterion, depending on conditions DS=1.10⁻⁴ to 1.10⁻², preferably 5.10⁻⁴ to 5.10⁻³, max. phosphorus content 0.14% (0.04% from cross-linking)

2. Dicarboxylic acid cross-linking 2 starch--OH→starch--O--CO--(CH₂)_(n) --CO--O--starch e.g. n=4: adipic acid cross-linking, max. 0.12% adipic anhydride

3. Glycerol cross-linking 2 starch--OH→starch--O--CH₂ --CHOH--CH₂ --O--starch max. 0.3% epichlorohydrin or 0.6% acrolein

The importance of cross-linking becomes apparent when observing the processes related to increasing swelling and gelatinization.

The water absorption, reversible up to approximately 50° C., and swelling of starch granules increases as the temperature rises. Partly crystalline structures are dissolved and viscosity increases strongly, as the increasingly swelling starch granules increasingly bind the free water. Parts of the starch, especially amylose, are released and serve as glue. As swelling continues, the swollen granules are destroyed and viscosity decreases markedly, especially in the case of potato starch.

This excessive swelling is to be prevented by slight structural cross-linking.

The preferable derivative according to the invention is:

1. a starch ether (hydroxypropyl ether): thereby swelling and gelatinization at lower temperatures and simultaneously

2. a cross-linked starch (phosphate-ester linkages): limiting and slowing down swelling, water being better bound, no bursting of the granular structure.

Other derivatives with similar characteristics are:

1) Starch esters for example with a) acetic acid, b) succinic acid, c) phosphoric acid, or d) alkenyl succinic acid; thereby earlier swelling and gelatinization.

2a) Cross-linking via dicarboxylic acid, phosphate and glycerin groups to limit swelling and bursting

2b, c) No chemical cross-linking, but free carboxylic groups, native or by substitution, such as from succinic acid, octenyl succinic acid. These groups also lead to products with greater density and strength due to coordination compounds with bivalent and trivalent ions (Ca, Mg, Al) and with silicates.

The degree of substitution of the starch derivatives should be less than 0.2.

Generally speaking, the gelatinization temperature should be lowered by at least 2° C., preferably 5° C., by derivatization to observe an effect.

With starch modified by ionic interaction, a "bridge function" similar to cross-linking may be assumed with the ionic groups stated below.

With the following substances an intensifying effect may be observed:

1. Aluminum sulfate An influence of aluminum ions was observed in the concentration range 0.05-0.15 g Al₂ (SO₄)₃ per 100 g starch. There is no analogy to the seizing of paper, as the batter pH is about neutral or above, conditions where aluminum hydroxide starts precipitating.

2. Alkali silicates Addition of water glass solutions in the range of 0.1-1.0% of starch leads to a significant structure consolidation. This happens despite the high pH of 7.5-9.0 in the batter, which normally causes an opposite effect.

3. Dicalcium phosphate, calcium silicate Dicalcium phosphate and calcium silicate also lead to a consolidation of the structure when added at 0.1-2.0% of starch. The little soluble salts have only a minor influence on the pH of the batter.

With other phosphates, such as monocalcium phosphate, tricalcium phosphate or pyrophosphates as well as other calcium salts no such effect can be observed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

Production of trays; 235×175×14 mm addition of potato starch succinic acid ester derivative

    ______________________________________                                         Ingredient/recipe no.                                                                            1        2        3                                          ______________________________________                                         Starch (1)        100      80       50                                         Water             100      100      100                                        Starch derivative (4)                                                                            --       20       50                                         Thickening agent (2)                                                                             0,5      0,5      0,5                                        Release agent (3) 2        2        2                                          Viscosity, mPas, 24° C.                                                                   1400     1500     3100                                       Baking time, sec. 155      160      190                                        Baking temperature, °C.                                                                   190      190      190                                        Weight, g         16,1     21,4     22,0                                       Weight, %         100      133      137                                        ______________________________________                                    

pH value 7,4; conditioning 70% r.h., 27° C., 24 hours. (1) potato starch; (2) guar; (3) magnesium stearate; (4) succinic acid ester of potato starch, 4% substitution

Resistance to compression test: testing the maximum force required to compress the specimens by 30% according to a relative method has shown the following results. Number of specimens per trial:

    ______________________________________                                                Weight     Maximum force                                                Recipe no.                                                                              g         N      %       s(1) s, %                                    ______________________________________                                         1        16,1       95    100     31   33                                      2        21,4      337    355     45   13                                      3        22,0      468    493     51   11                                      ______________________________________                                          (1) Standard deviation N, n = 10 (n = 9 with no. 3)                      

A bending test showed no significant differences in the force required to break the specimens.

EXAMPLE 2

Production of ampoule tray, 80×65×13 mm; addition of starch ether derivativ with phosphate cross-linking

    ______________________________________                                         Ingredient/recipe no.                                                                          4       5        6     7                                       ______________________________________                                         Starch (1)      100     90       70    --                                      Water           100     100      100   100                                     Starch derivative (4)                                                                          --      10       30    100                                     Thickening agent (2)                                                                           0,5     0,5      0,5   0,5                                     Release agent (3)                                                                              2       2        2     2                                       Baking time, sec.                                                                              32      33       36    44                                      Baking temperature, °C.                                                                 185     185      185   185                                     Weight, g       1,78    1,85     2,00  2,88                                    Weight, %       100     104      112   162                                     ______________________________________                                          conditioning 72% r.h., 26° C., 24 hours.                                (1) potato starch; (2) guar; (3) magnesium stearate; (4) hydroxypropyl         ether, crosslinked                                                       

EXAMPLE 3a

Rectangular cup, 110×120×48 mm; addition of alkali silicates

    ______________________________________                                         recipe no.                                                                               8       9       10    11    12    13                                 ______________________________________                                         Ingredient                                                                     Starch (1)                                                                               100     100     100   100   100   100                                Water     120     120     120   120   120   120                                Fiber (4) 10      10      10    10    10    10                                 Thickening                                                                               0,5     0,5     0,5   0,5   0,5   0,5                                agent (2)                                                                      Release   2       2       2     2     2     2                                  agent (3)                                                                      Soda      --      0,3     0,5   0,7   1     2                                  waterglass                                                                     Viscosity,                                                                               1500    1400    1300  1300  1200  --                                 mPas, 22° C.                                                            pH value  7,6     8,9     9,0   9,4   9,5   >10                                Baking    90      90      90    90    90    90                                 time, sec.                                                                     Baking    200     200     200   200   200   200                                temperature °C.                                                         Weight, g,                                                                               8,5     9,0     10,3  12,1  14    16                                 without cond.                                                                  Weight, % 100     106     121   142   (165) (188)                                                                    (5)   (5)                                ______________________________________                                          conditioning 70% r.h., 27° C., 24 hours.                                (1) potato starch; (2) guar; (3) magnesium stearate; (4) cellulose; (5)        partly formation of cracks                                               

EXAMPLE 3b

Rectangular cup, 110×120×48 mm; addition of alkali silicates

    ______________________________________                                         Ingredient/recipe no.                                                                          14      15      15a   16                                       ______________________________________                                         Starch (1)      100     100     100   100                                      Water           130     130     130   130                                      Fiber (4)       10      10      10    10                                       Thickening agent (2)                                                                           0,3     0,3     0,3   0,3                                      Release agent (3)                                                                              2       2       2     2                                        Potassium waterglass                                                                           --      0,5     1     0,5(5)                                   Calcium silicate                                                                               5       --      --                                             Viscosity, mPas, 22° C.                                                                 1300    1200    1400  1300                                     pH value        7,6     9,1     9,7   7,5                                      Baking time, sec.                                                                              90      90      90    90                                       Baking temperature, °C.                                                                 200     200     200   200                                      Weight, g, without cond.                                                                       9,5     9,7     11,0  8,7                                      ______________________________________                                          conditioning 70% r.h., 27° C., 24 hours.                                (1) potato starch; (2) guar; (3) magnesium stearate; (4) cellulose; (5)        neutralized with 12 ml 0,1 N hydrochloric acid                           

EXAMPLE 4

Production of flat tray, 235×175×12 mm, wall thickness 4 mm, different additions of potato starch derivatives

    ______________________________________                                         Ingredient/recipe no.                                                                          17       18      19    20                                      ______________________________________                                         Starch (1)      100      90      80    70                                      Water           100      100     100   100                                     Starch derivative (4)                                                                          --       10      20    30                                      Thickening agent (2)                                                                           0,5      0,5     0,5   0,5                                     Release agent (3)                                                                              2        2       2     2                                       Viscosity, mPas, 22° C.                                                                 2000     2200    2000  2000                                    Baking time, sec.                                                                              150      155     160   160                                     Baking temperature, °C.                                                                 190      190     190   190                                     Weight, g, without cond.                                                                       15,3     16,3    17,3  18,8                                    Weight, %       100      107     113   123                                     ______________________________________                                          conditioning 72% r.h., 25° C., 24 hours                                 (1) potato starch; (2) guar; (3) magnesium stearate; (4) potato starch,        hydroxypropylated, crosslinked                                           

EXAMPLE 5

Production of a basket-like container, 115×80×38 mm, different additions of hydroxypropylated potato starch

    ______________________________________                                         Ingredient/recipe no.                                                                          21      22      23    24                                       ______________________________________                                         Starch (1)      100     80      50    --                                       Water           100     100     100   100                                      Starch derivative (4)                                                                          --      20      50    100                                      Thickening agent (2)                                                                           0,5     0,5     0,5   0,5                                      Release agent (3)                                                                              2       2       2     2                                        Viscosity, mPas, 22° C.                                                                 1450    1800    3300  >10000                                   Baking time, sec.                                                                              60      55      55    55                                       Baking temperature, °C.                                                                 185     185     185   185                                      Weight, g       4,3     4,6     4,9   5,3                                      Weight, %       100     108     113   123                                      ______________________________________                                          conditioning 72% r.h., 25° C., 24 hours                                 (1) potato starch; (2) guar; (3) magnesium stearate; (4) propoxylated          potato starch                                                            

Resistance to compression test: testing the maximum force required to compress the specimens by 30% according to a relative method has shown the following results. Number of specimens per trial:

    ______________________________________                                                Weight of                                                                               Maximum force                                                  Recipe no.                                                                              tray, g    N      %      s(1) s, %                                    ______________________________________                                         21       4,3        128    100    17   13                                      22       4,6        155    121    17   11                                      23       4,9        160    125    22   14                                      24       5,3        173    135    35   20                                      ______________________________________                                          (1) Standard deviation N, n = 12                                         

EXAMPLE 6

Production of rectangular conical container, 145×90×50 mm; different additions of an octenyl succinate ester

    ______________________________________                                         Ingredient/recipe no.                                                                          25      26      27    28                                       ______________________________________                                         Starch (1)      100     90      80    60                                       Water           110     110     110   110                                      Starch derivative (4)                                                                          0       10      20    40                                       Thickening agent (2)                                                                           0,5     0,5     0,5   0,5                                      Release agent (3)                                                                              2       2       2     2                                        Viscosity, mPas, 22° C.                                                                 1500    1480    1520  1700                                     pH value        8,0     7,7     7,4   7,0                                      Baking time, sec.                                                                              70      68      60    58                                       Baking temperature, °C.                                                                 190     190     190   190                                      Weight, g       6,2     6,8     7,5   8,8                                      ______________________________________                                          conditioning 70% r.h., 10° C., 10 hours                                 (1) potato starch; (2) guar; (3) magnesium stearate; (4) corn starch,          octenyl succinate                                                        

Resistance to compression test: testing the maximum force required to compress the specimens by 30% according to a relative method has shown the following results. Number of specimens per trial:

    ______________________________________                                                Weight of                                                                               Maximum force                                                  Recipe no.                                                                              tray, g    N      %      s(1) s, %                                    ______________________________________                                         25       6,2         74    100    16   22                                      26       6,8        114    154    16   14                                      27       7,5        156    211    16   10                                      28       8,7        219    296    40   18                                      ______________________________________                                          (1) Standard deviation N, n = 10                                         

EXAMPLE 7

Production of rectangular conical container, 145×90×50 mm

    ______________________________________                                         Ingredient/recipe no.                                                                          29      30      31    32                                       ______________________________________                                         Starch (1)      100     75      75    75                                       Water           110     110     110   110                                      Starch derivative (4)                                                                          --      25      --    --                                       Starch derivative (5)                                                                          --      --      25    --                                       Starch derivative (6)                                                                          --      --      --    25                                       Thickening agent (2)                                                                           0,5     0,5     0,5   0,5                                      Release agent (3)                                                                              2       2       2     2                                        Viscosity, mPas, 25° C.                                                                 1750    1250    1800  3500                                     Baking time, sec.                                                                              75      67      63    63                                       Baking temperature, °C.                                                                 190     190     190   190                                      Weight, g       6,6     7,3     8,3   6,9                                      ______________________________________                                          conditioning 75% r.h., 12 hours, room temperature.                             (1) potato starch; (2) guar; (3) magnesium stearate; (4) corn starch,          hydroxypropyl ether; (5) corn starch, octenyl succinate; (6) corn starch,      cationic, hydrophobic                                                    

EXAMPLE 8

Production of round plate, diameter 155 mm, 12 mm high

    ______________________________________                                         Ingredient/recipe no.                                                                           33       34       35                                          ______________________________________                                         Starch (1)       100      --       --                                          Water            100      100      100                                         Starch derivative (4)                                                                           --       100      --                                          Starch derivative (5)                                                                           --       --       100                                         Thickening agent (2)                                                                            0,5      0,5      0,5                                         Release agent (3)                                                                               2,0      2,0      2,0                                         Baking time, sec.                                                                               60       70       75                                          Weight, g, without                                                                              6,0      9,5      10,5                                        conditioning                                                                   ______________________________________                                          conditioning 70% r.h., 27° C., 24 hours.                                (1) potato starch; (2) guar; (3) magnesium stearate; (4) corn starch,          cationic, hydrophobic; (5) corn starch, octenyl succinate                

EXAMPLE 9

Production of packaging trays, 130×105×30 mm

    ______________________________________                                         Ingredient/recipe no.                                                                         36      37      38     39                                       ______________________________________                                         Starch (1)     100     --      --     100                                      Water          100     100     110    100                                      Starch derivative (4)                                                                         --      --      100    --                                       Starch derivative (5)                                                                         --      100     --     --                                       Starch derivative (6)                                                                         --      --      --     10                                       Thickening agent (2)                                                                          0,5     0,5     0,5    --                                       Release agent (3)                                                                             2       2       3      2                                        Baking time, sec                                                                              90      90      115    90                                       Weight, g, without                                                                            8,9     13,0    18,0(7)                                                                               12,0                                     conditioning                                                                   ______________________________________                                          (1) potato starch; (2) guar; (3) magnesium stearate; (4) rice flour; (5)       corn starch, cationic, DS = 0,04; (6) corn starch, propoxylated,               pregelatinized; (7) isolated partial formation of cracks                 

EXAMPLE 10

Production of a tray, 135×220×19 mm; addition of different concentrations of Al ions

    ______________________________________                                         Ingredient/recipe no.                                                                           40      41      42    43                                      ______________________________________                                         Starch (1)       100     100     100   100                                     Water            100     100     100   100                                     Thickening agent (2)                                                                            0,5     0,5     0,5   0,5                                     Release agent (3)                                                                               2       2       2     2                                       Aluminum sulfate.xH.sub.2 O                                                                     --      0,11    0,22  0,44                                    55% Al.sub.2 (SO.sub.4).sub.3                                                  corresponding to Al.sup.3+                                                                      0       0,01    0,02  0,04                                    Batter volume, ml                                                                               30      32      34    37                                      Batter temperature, °C.                                                                  25      25      25    25                                      Viscosity, mPas, ± 100 mPas                                                                  1500    1500    1500  1500                                    Baking time, sec., ± 5 sek.                                                                  145     145     145   145                                     Baking temperature, °C.                                                                  190     190     190   190                                     Weight, g (average)                                                                             15,2    16,2    17,4  18,8                                    Weight, % (relative)                                                                            100     107     114   124                                     ______________________________________                                          conditioning 72% r.h., 12 hours, room temperature                              (1) potato starch; (2) guar; (3) magnesium stearate                      

EXAMPLE 11

Production of rectangular conical container, 145×90×50 mm

    ______________________________________                                         Ingredient/recipe no.                                                                        44      45     46    47    48                                    ______________________________________                                         Starch (1)    100     100    90    90    90                                    Starch (4)    --      --     --    --    10                                    Starch derivative (5)                                                                        --      --     10    10    --                                    Water         110     110    110   110   110                                   Thickening agent (2)                                                                         0,5     0,5    0,5   0,5   0,5                                   Release agent (3)                                                                            2       2      2     2     2                                     Aluminum sulfate.xH.sub.2 O                                                                  --      0,15   --    0,15  --                                    55% Al.sub.2 (SO.sub.4).sub.3 cor-                                             responding to Al.sup.3+                                                                      --      0,013  --    0,013 --                                    Viscosity, mPas, 22° C.                                                               800     800    850   1000  600                                   pH value      7,3     6,7    7,1   6,6   7,3                                   Batter volume, ml                                                                            15      15     17    17    16                                    Baking time, sec.                                                                            70      74     70    63    70                                    Weight, g (average)                                                                          6,83    7,17   7,31  7,38  6,92                                  Weight, % (relative)                                                                         100     105    107   108   101                                   ______________________________________                                          Baking temperature 180/185° C., conditioning 72% r.h., 6 hours,         26° C.                                                                  (1) potato starch; (2) guar; (3) magnesium stearate; (4) corn starch; (5)      corn starch derivative, octenyl succinate                                

EXAMPLE 12

Production of packaging tray, 130×105×30 mm

    ______________________________________                                         Ingredient/recipe no.                                                                        49     50      51    52    53                                    ______________________________________                                         Starch (1)    100    100     100   100   100                                   Water         110    110     110   110   110                                   Thickening agent (2)                                                                         0,5    0,5     0,5   0,5   0,25                                  Release agent (3)                                                                            2      2       2     2     2                                     Aluminum sulfate,                                                                            --     0,05    0,1   0,15  0,15                                  anhydrous                                                                      Viscosity, mPas, 22° C.                                                               1400   1700    1800  1900  900                                   pH value      7,7    7,1     6,7   6,5   6,3                                   Baking time, sec.                                                                            65     65      70    70    73                                    Baking temperature, °C.                                                               180    180     180   180   180                                   Weight, g (average)                                                                          8,3    8,7     9,6   9,0   9,8                                   Weight, % (relative)                                                                         100    105     116   118   118                                   ______________________________________                                          conditioning 72% r.h., 3 hours, 29° C.                                  (1) potato starch; (2) guar; (3) magnesium stearate                      

Resistance to compression test: testing the maximum force required to compress the specimens by 30% according to a relative method has shown the following results. Number of specimens per trial:

    ______________________________________                                         Recipe                                                                               Weight   specimen Al sulfate                                                                              Maximum force                                 no.   of g     %        g/100 g starch                                                                          N      %                                      ______________________________________                                         49    8,25     100      0        98     100                                    50    8,70     105      0,05     118    120                                    51    9,62     117      0,1      133    136                                    52    9,70     118      0,15     153    156                                    ______________________________________                                          (1) Standard deviation N, n = 10                                         

EXAMPLE 13

Production of packaging tray, 130×105×30 mm (as in example 12)

    ______________________________________                                         Ingredient/recipe no.                                                                            54       55       56                                         ______________________________________                                         Starch (1)        100      100      100                                        Water             100      100      100                                        Thickening agent (2)                                                                             0,5      0,5      0,5                                        Release agent (3) 2        2        2                                          Calcium carbonat  --       2        --                                         Calcium hydrogen phosphate                                                                       --       --       1                                          Viscosity, mPas, 22° C.                                                                   1500     1900     1300                                       pH value          7,6      8,9      7,3                                        Baking time, sec. 65       65       70                                         Baking temperature,                                                            conditioning as in example 12                                                  Weight, g         9,03     8,61     9,57                                       Weight, Relativ-% 100      95       106                                        Maximum force, N (4)                                                                             11,8     12,3     14,2                                       Maximum force, % (relative)                                                                      100      104      120                                        ______________________________________                                          (1) potato starch; (2) guar; (3) magnesium stearate; (4) measured at           punched disc, 30 mm diameter                                             

EXAMPLE 14

Production of a sorting insert, 195×65×16 mm

    ______________________________________                                         Ingredient/recipe no.                                                                           57      58      59    60                                      ______________________________________                                         Starch (1)       100     100     100   100                                     Water            120     120     120   120                                     Thickening agent (2)                                                                            0,3     0,3     0,3   0,3                                     Release agent (3)                                                                               2       2       2     2                                       Calcium hydrogen phosphate                                                                      --      1,2     --    --                                      Calcium phosphate                                                                               --      --      1,25  --                                      Calcium dihydrogen phosphate                                                                    --      --      --    0,9                                     pH value         7,4     7,1     7,0   6,6                                     Baking time, sec.                                                                               28-30   28-30   28-30 28-30                                   Baking temperature, conditioning                                               as in example 13                                                               Weight, g        5,01    5,55    5,45  5,37                                    Weight, % (relative)                                                                            100     111     109   107                                     ______________________________________                                    

EXAMPLE 15

Production of trays, 235×175×14 mm, addition of starch ester derivative

    ______________________________________                                         Ingredient/recipe no.                                                                            61       62       63                                         ______________________________________                                         Starch (1)        100      50       0                                          Water             100      105      110                                        Starch derivative (4)                                                                            --       50       100                                        Thickening agent (2)                                                                             0,5      0,5      0,5                                        Release agent (3) 2        2        2                                          Baking time, sec. 170      180                                                 (5)                                                                            Baking temperature, °C.                                                                   190      190      190                                        ______________________________________                                          pH value 7,2; conditioning 73% r.h., 24° C.; 24 hours                   (1) potato starch; (2) guar;. (3) magnesium stearate; (4) acetylated           potato starch, E1422; (5) no longer properly shaped                       

We claim:
 1. A process of manufacturing biodegradable, thin-walled baked shaped bodies in a multi-part baking mold, comprising the steps of(a) baking an essentially fat-free baking composition in the mold, the baking composition being composed of(1) 42.0-60.0%, by weight, of water, (2) 36.0-56.5%, by weight, of a starch product comprised of 0.0-54.5%, by weight, of a first starch base selected from at least one member of the group consisting of starch, various starches, a mixture of various starches, flour, various flours and a mixture of various flours, and 2.0-56.5%, by weight, of a second starch product selected from at least one member of the group consisting of a starch esterified with organic acids, a starch esterified with phosphoric acid, an etherified starch, a cross-linked starch and a starch modified by ionic interaction with an added salt, (3) 0.04-11%, by weight, of a release agent selected from at least one member of the group consisting of medium-chain and long-chain fatty acids and their salts, derivatives and amides, medium-chain and long-chain substituted fatty acids and their salts, derivatives and amides, and 0.5-6.5, by weight, of polymethylhydrogen siloxanes, (4) fibrous materials, (5) non-fibrous fillers, (6) colorants, (7) preservatives, and (8) antioxidants, and (b) conditioning the baked shaped bodies after baking to obtain a moisture content of 6-22%, by weight.
 2. The manufacturing process of claim 1, wherein the baking composition contains 10.0-50.0%, by weight, of the first starch base.
 3. The manufacturing process of claim 1, wherein the baking composition contains 2.0-28.0%, by weight, of the second starch base.
 4. The manufacturing process of claim 1, wherein the baking composition contains 0.2-4.5%, by weight, of the release agent.
 5. The manufacturing process of claim 1, wherein the baking composition contains 0.1-4.2% by weight, of the polymethylhydrogen siloxanes as the release agent.
 6. The manufacturing process of claim 1, wherein the esterified starch of the second starch product is esterified with a member selected from the group consisting of acetic acid, succinic acid, alkenyl-substituted succinic acid and phosphoric acid.
 7. The manufacturing process of claim 6, wherein the degree of substitution of the esterified starch is less than 0.2.
 8. The manufacturing process of claim 1, wherein the etherified starch of the second starch product is etherified with a member selected from the group consisting of ethylene oxide and propylene oxide.
 9. The manufacturing process of claim 8, wherein the degree of substitution of the etherified starch is less than 0.2.
 10. The manufacturing process of claim 1, wherein the cross-linked starch of the second starch product is a starch cross-linked with a member selected from the group consisting of sodium methaphosphate, phosphorus oxychloride, dicarboxylic acid, adipic acid, epychlorohydrin and acrolein.
 11. The manufacturing process of claim 10, wherein the degree of substitution of the etherified starch is less than 0.2.
 12. The manufacturing process of claim 1, wherein at least one member of the group consisting of aluminum sulfate, an alkali silicate, dicalcium phosphate and calcium silicate is added to the starch of the second starch product. 